Telephone trunking system.



PATENTED MAY 14, 1907 H. G. WEBSTER.

TELEPHONE TRUNKING SYSTEM.

APPLICATION FILED AUG. 1, 1902.

. To all whom it may concern.

UNITED sures PATENT OFFICE.

HARRY e. WEBSTER, OF CHICAGO, ILLINOIS, ASSIGNOR TO KELLOGG SWITCHBOARDAND SUPPLY COMPANY, OF CHICAGO, ILLINOIS, A

CORPORATION OF ILLINOIS.

,- TELEPHONE 'TRUNKING SYSTEIVL'V Specification of Letters Patent. I I vApplioatioufi le iAngust l, 1902. S erialNo.117,919.

fPat'e'nted May. 14, 1907;

Be itknown that I, HARRY G. WEBSTER,

a citizen of the United. Statesof-America,

and a resident of Chicago, county of Cook, and State of Illinois, haveinvented a certain new and useful Improvement in Telephone TrunkingSystems, of which the following is Specification. .7

i .My invention relates to tele'phone trunking systems adapted toconnect together for conversational purposes telephone lines terminatingat. different switchboard sections.

In anapplication filed by William W. Dean, June 28th, 1902, Serial N 0.113,581, atrunking system is shown extending between differentswitchboard sections at which terminate subscribers linesof the Dunbaror two My inventionirela'tes to trunk systems designed more particularlyfor usewithlines of the Dunbar or two-wire type atltlie outgoing. endand lines of the l -fthreei or four wire type at the incoming end.

' In lines of the former type, it is well known, the cut-off relays areactuated over a portion of the talkin circuit, while in lines of thelatter type, sue devices areactuated over entirely local circuits.-

Some ofthe novel featuresofmyinvention are capable of use in-variousrelations and al such uses are contemplated as heingf'withini the limitsof myimprovements" e xternal line circuit when the said cut-ofi re layis-energized. ."g At the central ofiice C, the usual'operator s Myinvention has for its objects the j' i'ovi Myinvention is i llustratedby the accompan'ying drawings in which Fi ure 11s a diagram ofsubscribers lines termlnating at difierent central ofiices with a cordcircuit at one officeand a trunk extend-' ing between said officestoconnect-the lines together for conversation; Fig. 2 is a modification ofthe outgoin end of the trunk, and" Fig. 3 is also a modi cation of. theoutgoing end.

Referrin plurality oi subscribers lines terminating at the centraloflice C, said lines beingofthe two-wire" or ,Dunbar type, This lineextends in two limbsfl and 3 from the subscriber s station A to the saidcentral emcee or SpI'l to Fig. 1, L designates one of a where itisfittedwith suitable answering and .multiple jacks or connectionterminals J, J

of a transmitter, 4, a receiver, 5, a ringer or call hell, 6, and thecondenser 7. a The switchhook, 8, is adapted in its normal position andwhen the receiver is placed thereon, to open the circuit through thetransmittere andreceiver 5 andto close it through the call bell G'andcondenser 7. A retardation coil 9 is connected at the sub-station whenthe, ho0k is raised,; in parallel with the receiver 5, and

condenser 7, to provide a path transparent -to-steady currents butopaqueto voice currents: The-line conductors 2 and 3 Include respectively thearmatures or springs lOand 11 of the cut-off relay R which is" permanently legged to ground from the sleeve c0ntacts 7' 7' of the jacks J, JThe armature gfilO is normally connectedwith ground oughthe conductor12',- while the [opposite armature 11-, is normally connectedwith-conductor 13 containing the line'relay R for the-line, saidconductor leading tothe live or ungrounded 'poleof the central bat- 'te.B the opposite olefofwhich isground- Gi The line relay 5 The forwardcontacts 14 and 150i the cut-off r'elay' R are adaptedto connect'thejacks and theswitchboard section OI thelinewiththe cord circuit isprovided, said cord circuit hav ing an answering p ug 'andi'awcauifigplug P, each being provided with atip contact 10 controls through its j'armature= the circuit of the line signal S.

and a sleeve contact p a dapted't o register with like contact surfacsjand 3' in the jacks of. the line when the plug is inserted therein.The'tip contacts of the plugs are connected together by means of the tipstrands t'and t of the cord circuit and the interposed con denser 0,while the sleeve contacts are like Wise connected by the sleeve strandssand .9 and-'the interposed, condenser 0 A con-.

'roo

ductor 16 extends from the grounded pole of the batteryflB to the tipstrand t and con-- tains the winding of the-tip supervisory relay 1*?associated with the answering plug P, while the live pole of the batteryis connected bv means of conductor 17 with the answering sleeve strandsand includes the Windingof the sleeve; supervisory relay rte-Theserelays 1* and-r serveto-control the. circuit of the supervisory lamp S vassociatedwith the answering plug P, the former relayserving'to normallyclose said circuit, ofthe lamp, While {the latter relay normally-iopens1 "the same. The battery B is associate-dwith the opposite orcalling-end of the cord circuit and is connected by conductors 18 and19With the.

; tip andsleevestrands t and s respectively,

the former conductor including'the Winding of the supervisory relay 1",while the latter conductor includes the similar relay 1' These relaysserve in a manner similar to the.

relays'r and T to control the circuit of the supervisory lamp Sassociated with thecallingplug P .The relays r and 1" are convenientlyre ferred to as the tip relays and relays r and r as the sleeve relays,since they are con-' nected with and operated by current flowing whenthe relay is energized. The back con-- tact 22 of this extra spring isconnected over the corresponding strands of the cord circuit. The tipstrand t of the callingplug and tes'tingplug P is normally open throughthe extra 'spr ing or movable contact 20 of the sleeverelay 11 but isadapted to be clo sed by the said spring and its forward contact 21,

" through the medium of conductor 23 with one side of the highresistance and high impedance relay 1", known as the? test relay,

the other side of which is grounded. The armature'of this relayis'likewisegrounded" and its forward contact isconn'ectd with the vprimary winding 'of the operators induction coil 25 by means ofconductor 24. The

I other end of the'saidr'i primary winding is conedium of conductor 26nected through the to the live pole of the battery B, a retarda tioncoil 27 being included in this circuit The operators transmitter'28is'joined on one side to conductor 26,-intermediate her primary-coil andthe coil 27, andon the other side through conductor '29 to ground. Acondenser c is included in the operators local circuit to facilitatetalking and is con? nected as shown, The secondary winding of herinduction coil 25 is adapted to be included together with her receiver30 and a condenser c in abridge between the strands of the cord circuitby means of any suitable key and in.-- dicated diagrammatically 'by'k,7c. Branch connections. 31 and 32 lead from opposite sides of thereceiver and secondary-to an ori der key connected-with an order circuitor wire 33leading to'the oflice 0% A grounded alternating currentringing generator '9 is adapted to be connected through a resistancelamp with the tip strand t of the, cord circuit by means of the tipringing key spring W, the sleeve contact-k of said key-being connectedwith battery lead 26 through wire 26 and-resistance 26 A trunkcircuit-is ShOWnIeXtending between the central oflices C and Csaid-trunk circuitbeing fitted :at the outgoing end with multiple jacksJ ,andJ.

tends inftwo limbs 35 and 36 to the central "oi-lice C where it isprovided with suitable This trunk ex means for testingthe' condition ofthe wanted subscribe'rs line, for ringing the desired sub s'criberand-With signals to enable the operator to properly attend theconnection. These trunk conductors 35 and 36-terminate at the' incomingoflice'in windings 'w and w of the repeating coil W and the interposedcondenser 0 A trunkrelay 1* of fairly low resistance is connected inf'aconductor, leading from the trunk conductor 36 to the Normally,

spring .81 carrying the back contact 82 of through the medium ofconductor 80, s ring 81', contact 84 and conductor 83 and is t ereforeoperated over the metallic trunk line. The opposite windings 10 and wof. the repeating coilW with an interposed condenser 0 are connectedbetween the tip strand t and the sleeve strand *s of the tlexibleend of"the' trunk circuit, said end-being herein: after-referred to as thetrunk cord. These strands, terminate in corresponding contacts 1) and pof the trunk plugl. The tip relay r is located in a conductor 36 leadingfrom.

the tip strand through the battery B to ground; The sleeve relay 1- islegged directly to ground by conductor 41 from the sleeve "strand s ofthetru-nk cord. These relays serve to control the signal circuits attheincoming' end of 'thetrunk' so that the operator is enabled toproperly attend the connection. These signal circuits comprisethebattery-lead 47 extending from the live pole of the battery, a conductor85including the ringing lamp S? and extending to the spring contact 51ofthe-sleeve relay r", the normal contact '86 of which is connected by aconductor -87' to the point 88. A parallel branch of the signal circuitextends from the battery lead 47. over conductor 89 thence through thepilot relay 4? and the disconnect and guard lamp S? andthence' to thespring contact 90 of the trunk relay r which is. normally connectedthrough its contact common conductor 92 leads to the forward contact 93of the tip relay 1-. An auxiliary branch of the signaling circuit iscompleted by a conductor 94 from the forward contact 95 of the trunkrela to the back contact 96 of the tip relay. thus be observed :91 withthe point 88. From this point 88 a that one parallel branch of the saidcircuit or circuits includes the ringing lamp S and is controlledthrough the contacts 51 and'86 of the sleeverelay; while the otherparallel parallel branches. The auxiliary branch 94- i is enabled tothrow ground upon the parallel branchcontaining the guard anddisconnectsignal only when the trunk relay is operated. It willtherefore be observed that whenever.

the sleeve relay is operated the ringing lamp circuit is open, that whenthe trunk relay isoperated the disconnecting lamp circuit is open at thetrunk relay 1 but is, ,closed upon the auxiliary branch 94. The operatorat thisend of the line is enabled to'connect her telephone with thetrunk c'ord by mea-ns of the key -7c,'7c, while the operator at theother exchange is enabled to connect hertelephone with the B operatorbymeans of. the instruction circuit 33. A, ringing generator 9 is shownconnected with the tip'ringing contact k the resistance lamp being incircuit therewith, while the sleeve-key k is grounded as shown. Thesubscribers .lin'e .Lshown in connection with the ethos C is. ofthe typeemploying three or four wires andextending throughout the switchboardforthe opera-' tion of the busytest and theycut-ofi relay.

This line includes conductors-2 and 3 eXtending to the subscribersstation D, whilethe receiver 5 and transmitter 4"are included in seriesin the line when the telephone is off the hook, but when the telephoneisup'on' I current will'seek the grounded pole of the the hook',-the tipline conductor 2is connected with the grounded signaling bell '6. Inthis 4 conductor 47 to the live When the cut-off relay is actuated,-

acksl I the tout-off relay which is grounded through instance the tipspring 10 of the cut-off relay R is normally, grounded while the sleevespring I 11 normally leads through the line annunciator S7 which isconnected by the polelof the battery B however, these springs areconnected through their forward contacts 14 and 15 with the tip andsleeve contacts j and i of the connecting A third contact 11 is providedfor a resistance coil 11 and the forward contact of which connects byconductor 11? with the test rings 7', ji, of the jacks which aredesigned insulated from the line even when the plug is inserted in thejack, current from the main battery B flows through the cut-off relay Rto operate the same, to disconnect connects the, line signaling deviceand connect .the line limbs to the main contacts of the jacks.

I J ,;J and J J, are respectively busy back and dont'answer jacksassociated with the incoming trunks. comprises an induction coil 67having its primary in'circuit with the rapidly rotating circuit breaker68 and, the battery B, this battery being preferably the same as batteryB but shown separately for convenience. The secondary of theinduction-coil 67 is connected in circuit with the rapidly rotatinginterruptei169 and the more slowly operating interrupter 701 Frominterrupter 69 a conduct'or'71 leads to the sleeve'con-tacts ofthe busyback jacks J Jf, through-a 50 ohm resistance coil 72, while interrupter7 0 is connected byconductor 73 through resistance- .coil 74 to'thesleeves of the dont answer iacks, J J The tips of'both se'ts of jacksare united by conductor 75 with a groundedipole of the battery. The"circuit breaker 68 cause'sinduced currents in the secondary circuitswhich are interrupted at'short inter- This apparatus vals =by breaker69and-at longer intervals by breaker 70 to cause distinctive tones inthe receiver of the waitingsu'bscriber when the trunk plug-is insertedin'one or the other of the jacks. The circuit breakers 6 9 and 70 servealso to-gmake and break thecircuit of the supervisory relay 1" wherebythe supervisory signals at both ends of the trunk are flashed inaccorda'ncefwith the interrupted current.

- In tracing the circuits hereinafter, the plan of pointing outth'e'path for current from -the 'live or ungrounded pole of the batteryto the ground only will. be followed forl convenience, it beingunderstood that the return permits currentto f lowfrom thebattery Bthrough conductor 13, line relay'R spring 1 1 of cut-0E rlayR, limb '3of the telephone line, through the retardation coil 9 and transmitter 4at thesub-station, and thence over limb Zback to the central office andspring 10,. ofcut-orf relay B through conductor 12 to ground. The linerelay R is'thus operated and closes the circuit of the signal- .lamp Sto ground from the conductor 13.

The opera'tor'upon seeing the line signal exposed inserts the answeringplug P into the answeringljack J ofthe subscribers line and er telephone30 with the cord cir- IIC . cuit by depressing the listening key 7c, It,to

receive the order from the subscriber. insertionof the plugP closesacircuit thron h the cut-off relay'R from the live pole of t e battery Bthrough conductor 17, sleeve supervisory relay 1, sleeve strand 8,sleeve contacts 39 and 7' of I the plug and jack, thence through thewinding of the cut-.ofirelay R toground. The operation of this ree laydisconnects the armatureslfl and 11 from the ground wire 12 and from thebatterylead 13 and connects themethroughthe circuit of the supervisorysignal S which is; associated with the plug P,,but it is prepurposes.

vented from glowi-ngby the operation of the tip supervisory relay 1'which 1s connected in. the conductor 16- and receives currentover'telephone line and the tip strand't of the cord circuit and through theconductor 16 to the grounded 1 )le of the battery B, as soon as thecutrelay R is operated. The su er-- visory signal S therefore remainsinert-W 'le the battery B" furnishes ;cur rent':over the' metallictelephone line for the operation 'of the supervisory relays and forconversational The operators transmitter 28 is receivlng current at thistime from the bat- 'tery B over the conductor 26 through retardationcoil 27, thence through the transmitter 28 and over conductor 29 toground. When sound waves strike the transmitter 28, the current flowingtherethrough is varied which causes a variation of the charge in thecondenser and a corresponding surge of current through the primary ofher induction coil 25; These induce voice currents in the'secondarywhich are transmitted to the line and the operator is'therefore able toconverse with the calling subscriber. Upon learning that a subscriber inthe exchange C is desired, the A operator depresses theorder key toconnect her telephone with the order wire or circuit 33, and re eats thenumber of the wanted subscriber to t e B operator whose head telephone50 is permanently connected with the said order wire. The latter operator designates to the A operator the trunk to .be used for theconnection and.

roceeds to. test the condition of the wanted iine with the tip of theplug of the incoming trunk named. If the line is idle, no 4 click willbe received, but if busy, the test rings y" of the jacks will beconnected to round through the spring 11*- of the cut-o relay andresistance coil 11 to ground.. As before explained the tip of thetesting plug is con nected through the tip strand of the trunkcord,.conductor 36?,tip'relay r and battery B to ground. A completecircuit will therefore be established when the tip of the plug is Thetouchedto the test ring ofthe busydine,

which will-cause a flowof current and willaffect'the receiver of the Boperator, which is connected across the trunk cordcircuitby- 'means oftheikey k, k, sufficientl to indicate to her that the line is busy. theline idle the plug P is inserted in one of- };he multiple acksof'thewanted subscribers ine.

number of the trunk, to be used inserts the calling. plug P -of her cordcircuit in the trunk .jack J at her section at substantially the The Aoperator-having received the same time that .the trunk .plug isconnected with the called line The insertion. of the cord circuit plug 1closes a circuit from the live pole of the battery'B at the A officethrough conductor '19 sleeve supervisory relayr sleeve strand 8 of thecord circuit sleeve contact of the plug and jack and over the sleeve'conductor 36 of the trunk to the cen tral ofiice' C thence throughconductor 80 and r the trunk relay r over spring 81 and contacts 82 and42 of the sleeve relay 1' to ground:

Current over this path actuates the sleeve supervisory relay r in the Acord circuit which attracts its armatures and cuts out the test rela r"and completes the tip strand of the cor circuit througharmature 20 andits forward contact 21. The supervisory signal'S associated with thecalling plug 1? of the A cord circuit is therefore lighted b currentfrom the live pole of the battery 12 flowing over the conductor 26 andthrough the signal lamp Stand the armatures of the two supervisoryrelays to ground. This lamp is therefore lighted and remains lighteduntil the-re- Ioo' spouse of the called subscriber as hereinafter Iexplained.

The trunk relay 1 is also operated at this time by current over the pathjust traced which closes its contacts and and breaks contact 91 andwould operate the disconnecting signal S except for the fact that -thetiprelay 1" is now operated by current from .the battery B overconductor 36 a through the said relay, the tip strandfi, the

tip conductor 2 of the subscribers lineland through the groundedsignaling bell 6'. This relay therefore operates and closes circuit uponits forward contact 93 and since the sleeve relay 2 is not yet operated,it completes the ground cpnnection of the parallel signaling branches sothat the ringing lamp S the continuit of whose circuit is con- 1 trolledby the sleeve relay r", is-now lighted. Ringing current for thesubscribers line is furnished by the generator 9 over the ti sideofthelinc and through the bell 6, and s ould the-- subscriber respondduring ringing, the

current traverses back to the central office. "over'the sle'eve side ofthe line andthrough the grounded ringing key is in the sleeve strand ofthe cord When the subscriber respends a path for current from thebattery B over the metallic line is provided through the tip relay andthe tip strand of the cord, thence strand of the cordthrough conductor41, the

' which opens its contacts 4:2,and 82 thus break ing' the groundedtrunk-rela y operating cirsame time.

- necting 1am "which indicates to the operator that t e called cuit ofringing lamp S is opened atjcontacts ,51 and 86 of the sleeve relay 7'Whi ch indicates the hook','the supervisory lamp S is lighted, and whenthe subscriber-D, hangs uphis tele conditions just described and servesto cut- .is lighted. At the same time the ringing draws the-plug Whomthe jack of .thesub and a trunk-plug is inserted in the subscrib- .linewhen a cord circuit is not connected over .the tip line conductor andthrough the subscribers instruments andf'back over the sleeve conductorof the line and the sleeve sleeve relay rto ground and'the other side ofthe battery. This current flows in suflicient quantity to also:actuate'the sleeve relay'r cqit and closing contacts 81 and 84 wherebythe trunk relayis includedin the metalliecin .cuit of the outgoing endof the trunk and per-'1 mi'ts current to Ifiow from thebattery B of theA cord over the metallic trunk and back to the A office therebyoperating the supervisory, relay I -connected with theA cord to open thecircuit of the 'superviso signal subscriber has responded. Likewise thecirthe same fact to. the B operator. .The subscribersare now incondition for conversation and all supervisorylamps are extinguished.-When the A subscriber returns his receiver to phone, current is cut-offfrom the sleeve relay r which permits the re-establishment of the ofl'current from the supervisory relay 1 at the A ofiice whereby-thesupervisory signal S? scribers line. This de-energizes the tip relay 7'which disconnects the ground branch from the parallel'signaling branchesandretires all signals." f i The disconnect lamp S may be employed. as aguard lampin case a mistake is made ers line or incase the A' operatorconnects with a wrong trunk. thelatter case, the trunk relay 7' oftheline, is operated which closes the auxiliary branch 94 upon theparallel signaling branch containing the disconor guard lamp S which istherefore lig ted together the ilot signal and indlcates the fact of a'mistalieto the B operator. a

The insertion of the plug P in-a jack of a with the trunk at theopposite end results in establishing the disconnecting j conditionheretofore described, that is, the grounded 'branch 92 isclosed uponboth of the parallel 'signalingbranches whereby both lamps S and Slight.

; 1 la case the wantedsubscribers line is found busy or ifa subscriberhaving been called does not-respond, the. plug 1 is inserted in the jackJ or J and a correspond .ing signal is transmitted to the Waitingsubscriber. "Upon the insertion of plug P In one of the busy backordontanswer 'acks, for

example, one 0. the jacks-J a pat for ourrent is provided from thebattery 13 through the tip strand'of thetrunk cord, theti contacts ofthe plug andj ack and over con uctor 75 to ground. Q This will serve tooperate the t1 relay 1 toiconnect ground upon the pare al el signalingbranches. In the rotation of thecircuit breaker 69 a ath 'for current isalso rovided from the l ve pole of the battery g over the secondary" ofthe induction coil 67 and contacts of the circuitbreaker 69 :thenceoverithe conductor 71' and the sleeve strand of the trunk cord throughthe sleeve relay 1";to ground. This relay will therefore operate inaccordance with the,

interrupted currentto break the grounded circuit of the trunk conductor1 and complete' 113$; metallic circuit over -both.s ides of the outgoingend of the trunk wherebythe "supervisory; lamp 8- at the A'exchange isflashed in accordance with said interrupted current; The subscriber issimultaneously notified of the condition of the wanted'line by the tonecaused by the rapidly interrupted current. r The order circuit 33, as isindicated by the branch lines 33 connects the B operator with severaloperators either at the same or at diiiereht exchanges. The A o eratoris also provided with a plurality of eye Jc to connect herself withseveral B operators. The busy back or dontanswer apparatus is common tothe various sections of the incoming trunklboard, asis indicated by, theI branching lines; v p p Although 'I havedescribed the method of makinconnections through the medium of the or er circuit, I do not wish to soconfine the invention for it isapparent that. the A operator is able. bymeans of her testing appa ratus to test the condition of the several.trunks before her until an idle trunk is found, and upon findin j thesame,, she may connect the calling plug 15 of her cord circuit {with thetrunk, which would operate the trunk relay 1 at the incoming end v andlight the lamp S rwhich would then serve as a calling, lamp. The Boperator upon seeingthe signal, would depress her listening key k, k,andupon learning the order would make the deslred connection, ashereinbefore described. It

a that subscriber would have been tested in the 7 before the groundcircuit is opened,.the sleeve v will also be understood thathad a, Asubscriber called for a connectionwith another subscriber in the sameexchange, the line of of such coil it would not be necessary for thecontacts 81 and 84 at the Bend of the trunk to make contact beforebreaking contact at points 82 and 42 as is necessary with thearrangement shownin Fig. 1, where, if the me.- tallic circuit of thetrunk be not completed supervisory relay in the A cord may becomede-energiz'ed. In case of ground currents which may fiow in suchstrength as to operate the trunk relay when a retardation coil isemployedat the outgoing end of the trunk, the device shown in Fig. 3 maybe employed in which the retardation coil 34 is connected with a spring7' of the trunk jack J whichis normally disconnected from the.sleeveconductor, but which, upon the insertion of the connecting plug islifted by the ti spring into contact with the sleeve side. nder normal.conditions therefore" the retardation coil would be disconnected andearth currents could notaifect the trunk relay. The ground connec-vtions hereinbefore referred to, it will be understood, may be and inpracticeusually are one and the same, or they may be the common officefeturn, although it is found by ex-. 'perience that it is necessary toplace a dead ground upon one side, of the common battery which groundconnection may be placed at the opposite pole of the several batteriesinstead of as shown in the diagram, all of which is apparent to thoseskilled in the art.

Having thus described my invention, what I claim and desire to secure byLetters Patent is 1..The combination with a trunk circuit extendingbetween diflerent switchboard sections and adapted to connect telephonelines together for conversation, of a disconnect signal for the incomingend of the trunk, a

' source of current and a relay'associated with tions and adapted toconnect telephone lines. together for-conversation, of a ringing signalfor the incomin end of the trunk, a relay actuate'd over the tip side ofthe talking circuit and ground adapted to direct current through said sial to operate the same when the subscriber i response, and a secondrelay operated by ouras been called but 'before his rent flowing over aportion of the talking cir-,

cuit but having its coil out of the path of the voice currents, saidrelay being adapted to deprive said signal of. operating current whenthe'subs criber responds, substantially as de- I scribed.

. 3. The combinationwith a trunk circuit extending between differenttwitchboard sections and adapted to connect telephones line together forconversation, of a ringing signal for the incoming end of the trunk,arelay actuated over one'side of the telephone line and through thegrounded signaling bell to direct current through said signal to operatethe same when the subscriber has been called, *and a second relay atsaid end adapted to deal of operating current when prive said si thecalled su scriber responds,'substantially as described.

4. The combination with-a trunk circuit I extendin betweendiiferentswitchboard sections an adapted to connect lines together forconversation, of a ringing "signal for the incomin end of. the trunk, arelay and a source 0 a current connected with the tip side of the trunkcord, a grounded signaling bell from the tipjside of the subscribersline, said relaybeing actuated by current from said source over the tip.side of a cord and line and through the said grounded bell to cause theoperation of said signal when the connection is established with thecalled line, and a second relay connected with sleeve strand'of thetrunk cord and responsive to current in the metallic line when thecalled subscriber answers, said latter relay serving to render saidringing signalinoperative, substantially as described,

5. The combination with a trunk circuit extending between differentswitch-board sections and adapted to connect telephone lines togetherfor conversation, of a signal associated with the incoming end of. the

trunk, a relayalso at the incoming end adapted to be operated by currentsent over the trunk from the outgoing end, a second relay at saidincomin lend adapted to be operated by current owing over o,ne.si de othe called telephone line to the sub-station and ground when theconnection is establishe with the said called line, said relays jointlycontrolling said signal so as to operate the seam to give a guardindication when the connection is established. at the outgoing end ofthe trunk andv the trunk is discor nected from the called line, or toplace said described.

6. The Combination with a trunk circuit extending between different vswitchboard sections and adapted to connect telephone lines together forconversation, of a signal associated with the .incoming end of thetrunk, a relay also-at the incoming end operated by current overaportion of the tip side of the talking circuit when the connection isestablished with the called line,'a second relay at the incoming endactuated when. the connection exists at the outgoing end, said relaysjointly controlling said signal so as tooperate the same to give a guardindication when the connection is established at theoutgoing end of thetrunkand severed at the incoming end, or to place said signal incondition to operate'to give'a disconnect indication when the connectionis severed at the outgoing end and is completed at the incoming end,substantially as described.

7. The combination with a trunk circuit extending between differentswitchboard sections and adapted to connect telephone lines together forconversation, of a guard signal for the incoming end of the trunk, meansto actuate said signal by current sent over the trunk when theconnection is 1 established at the outgoingend of the trunk,

- the sub-station for rendering said and further means actuated bycurrent sent over a portion oithe talking circuit including one side ofthe telephone line tog-round at signal inert, substantiallyas described.

8. The combination with a trunk circuit extending between differentswitchboard sections and adapted to connect-telephone lines together forconversation, of a guard signal for the incoming end ,of the trunk, arelay to place 'said signal in condition to 0perate and actuated bycurrent sent. over the trunk, and a relay actuated by current over aportion of the tip side of the talking circuit when connectionis madewith the calledline for rendering said signal inoperative, substantiallyas described.

9. The combination with a trunk line ex tending between differentswitchboard sections and adapted to connect telephone lines together forconversation, of a supervisory signal. associated with the outgoing endof the trunk, a relay associated with the incoming end and connectedwith the sleeve strand ofthe trunk cord and responsive to current in themetallic talking circuit when the trunk is connected with the calledline, a source of distinctive signaling current with which the incomingend of the trunk is connected when a subscriber is busy or fails torespond, means for intermittently operating said relay when the trunk isconnected with said source, and means operated by said relay tocorrespondingly operate said supervisory signal, the waiting subscriberbeing also notified of the condition of the line by the distinctive tonein his receiver, substantially as described. r

10. 'T hecombination with a trunk line extending between differentswitchboard sections and adapted to connect telephone lines together forconversation, of a supervisory signal associated with the outgoing endof.

the trunk, the outgoing'end of the trunk being open to steady currentand one side thereof connected to ground, said signalbeing placed inoperative condition by current flowing over said side of the trunkcircuit to ground, and a relay at the incoming end connected with thesleeve strand. of the trunk cord actuated when the called subscriber.responds for disconnecting said ground'and connecting the two sides ofthe trunk'together to permit current to flow over both sides thereof torender the said supervisory signal inoperative, substantially asdescribed.

Signed by me at State of Illinois, this 28 Chicago, county of Cook,

day of July 1902.

, H. G. WEBSTER.

' Witnesses:

ROBERT LEwI-s 'AMn's, F. DUNBAR.

